1. Field
The present disclosure relates generally to electrosurgery and electrosurgical systems and apparatuses, and more particularly, to a return electrode detection and monitoring system and method thereof.
2. Description of the Related Art
Electrosurgery is a term used to describe the passage of high-frequency (i.e., radio frequency) electrical current through tissue to create a desired clinical tissue effect. Through this technique, the target tissue, acting as a resistor in an electrical circuit, is heated by its conduction of the electrical current. Electrocautery, as distinguished from electrosurgery, uses an electrical current to heat a surgical instrument, which in turn conveys that heat to the target tissue. Electrosurgical electrode tips remain cool while targeted tissues heat up, primarily because the electrodes have much lower impedance than the adjacent targeted tissues. Electrosurgical tissue effects include cutting, coagulation, desiccation and fulguration. In addition, modern electrosurgical generators can create blended modes of operation under which a surgeon can for example, cut and coagulate simultaneously.
In electrosurgery, there are two types of electrodes: mono-polar and bipolar. Mono-polar electrodes pass RF electrical current from an electrosurgical generator through an active electrode into targeted tissue, through the patient, a dispersive electrode (e.g., a return electrode or pad), and back into the electrosurgical generator. If the return electrode is properly placed relative to the patient and surgical site, the electrosurgical tissue effects occur only at the active electrode and not the dispersive electrode. On the other hand, bipolar electrodes are arranged in pairs (or poles, “+/−” and “−/+”) and form part of the surgical instrument (e.g., electrosurgical forceps) without the need for a separate return electrode (grounding) plate attached to the patient. The intended flow of current is between the pair of bipolar electrodes (from “+/−” to “−/+”), which are usually close together and use relatively low voltage.
In monopolar electrosurgery, the patient return electrode is placed at a remote site from the active or source electrode and is typically in the form of a pad adhesively adhered to the patient. The return electrode has a large patient contact surface area to minimize heating at that site since the smaller the surface area, the greater the current density and the greater the intensity of the heat. That is, the area of the return electrode that is adhered to the patient is important because it is the current density of the electrical signal that heats the tissue. A larger surface contact area is desirable to reduce heat intensity. Return electrodes are sized based on assumptions of the maximum current seen in surgery and the duty cycle (the percentage of time the generator is on) during the procedure.
The first types of return electrodes were in the form of large metal plates covered with conductive jelly. Later, adhesive electrodes were developed with a single metal foil covered with conductive jelly or conductive adhesive. However, one problem with these adhesive electrodes was that if a portion peeled from the patient, the contact area of the electrode with the patient decreased, thereby increasing the current density at the adhered portion and in turn increasing the heat applied to the tissue. This risked burning the patients in the area under the adhered portion of the return electrode if the tissue was heated beyond the point where the circulation could cool the skin.
To address this problem, split return electrodes and hardware circuits, generically called Return Electrode Contact Quality Monitors (RECQMs), were developed. Typically, these split electrodes consist of two separate conductive foils or plates connected by a resistive element and are usually referred to as resistive type return electrodes. The hardware circuit uses an AC signal between the two electrode halves to measure the impedance therebetween. This impedance measurement is indicative of how well the return electrode is adhered to the patient since the impedance between the two halves is directly related to the area of patient contact. That is, if the electrode begins to peel from the patient, the impedance increases since the contact area of the electrode decreases. Current RECQMs are designed to sense this change in the contact impedance (between the two plates) so that when the percentage increase in impedance exceeds a predetermined value or the measured impedance exceeds a threshold level, the electrosurgical generator is shut down to reduce the chances of burning the patient. However, in situations where the impedance is within predetermined limits but full contact between the body of the patient and return electrode is not achieved, the power output of the electrosurgical generator is substantially the same when using a resistive type return electrode. In the resistive split or non-split electrode, the electrode is always touching the patient, so the power delivery is not affected however the contact impedance between the two plates or electrodes affects the current density. Increased current densities could lead to patient burns on the applied sites.
In the case of a capacitive return electrode, which is used in the 4 MHz range of a electrosurgical generator's working frequencies, the capacitance of the contact between the body and the return electrode could affect significantly the power output of the electrosurgical generator. In other words, being in series with the body resistance, the contact capacitance will increase or decrease the overall load impedance, changing the voltage drop across the body impedance, thus changing the power delivery, hence the tissue effect.
Therefore, a need exists for techniques for determining contact quality in an electrosurgical unit while using a capacitive type return electrode. Furthermore, a need exists for a apparatus for supplying electrosurgical energy that is compatible with both resistive and capacitive type return electrodes.